Method for cutting a window in a vertical sheet of material, especially sheet metal

ABSTRACT

A method for cutting a window in a sheet of material that is held in a vertical plane. The cut is obtained by moving a cutting head that emits a fluid along a closed cutting run ( 14 ) that defines the outline of a piece of waste material ( 18 ). The run ( 14 ) returns to its starting point situated above a horizontal axis ( 22 ) passing through the barycenter ( 20 ) of the piece of waste material ( 18 ) and preferably situated in the vicinity of a vertical ( 24 ) passing through the barycenter.

TECHNICAL FIELD

The present invention relates to a method for cutting a window in avertical sheet of material, especially sheet metal.

More precisely, the invention relates to the operation of cutting—bymeans of a laser, for example—sheets held in a vertical plane.

BACKGROUND ART

A plant for cutting and bending pieces of sheet metal in which thesheets are cut in a vertical plane is described in the Italian patentapplication No. T095A000569 in the name of the present applicant. Ascompared with cutting operations in which the metal sheet is held in ahorizontal plane, cutting in a vertical plane is associated with theadvantage that the plant comes to occupy a smaller floor space and thatthe equipment needed to support the work piece is simplified.Nevertheless, cutting sheets of sheet metal while held in a verticalplane brings with it a series of problems that are not encountered inthe more traditional case in which the sheet to be cut rests on ahorizontal table.

One of these problems occurs in the case in which windows have to be cutin metal sheets held in a vertical plane. Hereinafter, in both thedescription and the claims, the term “window” is intended to refer toany aperture passing through the sheet, no matter what its shape.Cutting a window inevitably entails the production of a piece of wastematerial. When the metal sheets are held in a vertical plane, thesepieces of waste material can interfere with the cutting process. Infact, these pieces of waste material could fall towards the lasercutting head and thus become entangled with it or cause damage;alternately, they could remain on the sheet to be cut and protrude inthe direction of the cutting head, which is particularly liable tohappen in the case of sheet metal of considerable thickness, once againbecoming entangled with the laser head or causing damage to It. Theserisks become considerably greater when the pieces of waste material havea generally concave form or parts that either protrude or are recessed,because this will considerably increase the possibility of the piece ofwaste material becoming entangled with the work piece at the end of thecut of the window.

DISCLOSURE OF INVENTION

The present invention has been achieved with such a point in mind.Therefore, the object of the present Invention is to provide a methodfor cutting a window in a vertical sheet of material, especially sheetmetal which overcome s the said problems and drawbacks.

According to the present invention, the object as aforesaid is attainedby a method having the characteristics set out in the claims attachedhereto.

The innovative concept on which the present invention is based consistsessentially of defining a cutting run that returns to its startingpoint, the said starting point being situated above a horizontal axispassing through the barycentre of the piece of waste material.

Thanks to this solution idea, the pieces of waste material will fall onthe side of the metal sheet opposite to the side on which the lasercutting head is being operated, this by virtue of the well known factthat the laser beam is accompanied by a gas jet at a relatively highpressure.

The point at which the cutting run commences and closes is preferablysituated above a horizontal axis through the barycentre an d in thevicinity of a vertical axis through that centre, because this willfacilitate the piece of waste falling without performing a turningmotion.

In the case in which the window to be cut is either of a concave shapeor has parts that either protrude or are recessed, the cutting of thewindow is subdivided in such a way as to cut several pieces of wastematerial that are devoid of both protrusions and recesses. Each of thepieces of waste material is cut as previously described, that is to say,with a cutting run that closes at its starting point, this point beingsituated above a horizontal axis through the barycentre and, preferably,also in the vicinity of the vertical axis through the barycentre of thepiece of waste material.

BRIEF DESCRIPTION OF DRAWINGS

Further characteristics and advantages of the present invention willbecome apparent in the course of the detailed description given below,which is provided purely by way of non limitative example, withreference to the following drawings attached hereto, wherein

FIGS. 1, 2 and 3, show schematically the cutting sequence employed whena window is cut in accordance with the method of the present invention;

FIGS. 4 and 5, illustrate situations of entanglement of pieces of wastematerial that result from the cutting of windows of a generally concaveshape; and

FIG. 6, shows schematically the cutting sequence adapted to solve theseentanglement problems.

BEST MODE FOR CARRYING OUT THE INVENTION

There will be detailed below the preferred embodiments of the presentinvention with reference to the accompanying drawings. Like members aredesignated by like reference characters.

FIGS. 1 to 3 schematically illustrate the cutting sequence for cutting awindow of, say, quadrangular form in a metal sheet 10 that is being heldin a vertical plane. The cutting operation is carried out by moving aschematically indicated cutting head 12 capable of emitting a fluidwhile in use, which could—be for example—a laser focusing head or aplasma or water jet cutting head, along a cutting run 14 that definesthe outline of the window 16. The cutting run 14 likewise defines theperimeter of a piece of waste material 18 whose barycentre is indicatedby the reference number 20. Also show in the figures are two axespassing through the barycentre of the piece of waste material 18, one ofthese axes being horizontal 22 and the other vertical 24.

According to the present invention, the cutting run 14 that defines theoutline of the piece of waste material 18 returns to its starting point26 situated above the horizontal axis through the barycentre 22 andpreferably situated either on or in the vicinity of the vertical axisthrough the barycentre 24.

During the cutting operation, which in the present form ofimplementation will be assumed to be performed with a laser, the laserbeam is accompanied by a gas jet consisting of oxygen, nitrogen and amixture of other gases at a pressure that will generally range betweenabout 1 and 10 bar, but in certain cases may also reach 20 bar. When thecut is terminated in a zone situated above the axis 22 and preferably inthe vicinity of the axis 24, there is a very good probability that thepiece of waste material 18, thanks to the action of the said gas flow,will rotate around a horizontal axis parallel to the axis 22 through thebarycentre and eventually drop on the side away from the cutting head.In this way one avoids the pieces of waste material falling against thecutting head and the consequent risk of their becoming entangled withthe cutting equipment or causing damage to it.

FIGS. 4 and 5 illustrate the problem that may be encountered whencutting a window having the generic shape of a “C”. In this case, evenwhen one adopts the method described hereinabove, the piece of wastematerial 18 still has some probability of becoming entangled with thesheet of material from which it has been cut, thereby creating anobstacle as far as movements of the laser focusing head 12 areconcerned. In general, a problem of this type will occur in all cases inwhich the window is of a generally concave shape or comprises eitherprotruding or recessed parts, as is the case of shapes in the manner ofa “C”, an “L”, a “T”, a “V”, etc.

As schematically shown in FIG. 6, in these cases the window 16 issubdivided in such a way that the cutting operation gives rise toseveral pieces of waste material, indicated in the figure by thereference numbers 18 a, 18 b and 18 c. The number and the shape of thepieces of waste material 18 will depend on the shape of the window it isdesired to cut. In all cases, however, the shape of the individualpieces of waste material 18 a, 18 b, 18 c is such as to be wholly devoidof protrusions and recesses. The individual pieces of waste material arecut in succession and independently of each other, using the previouslydescribed cutting method illustrated by FIGS. 1 to 3. More precisely,each of the pieces of waste material 18 a, 18 b, 18 c that make up thewindow 16 is cut by following a cutting run that returns to its startingpoint situated above the horizontal axis 22 a, 22 b, 22 c passingthrough the barycentre of the pieces of waste material 18 a, 18 b, 18 c.Preferably, moreover, the starting and closure points of the cuttingruns will also be situated in the vicinity of the respective verticalaxes 24 a, 24 b, 24 c of the said pieces 18 a, 18 b, 18 c.

While preferred embodiments of the present invention have been describedusing specific terms, such description is for illustrative purposes, andit is to be understood that changes and variations may be made withoutdeparting from the spirit or scope of the following claims.

INDUSTRIAL APPLICABILITY

As stated hereinbefore, the method for cutting a window in a sheet ofmaterial, especially sheet metal according to the invention isapplicable for use in cutting machines, especially for a laser cuttingmachine which comprises: a clamping device for supporting the sheetmetal to be cut in a horizontal or vertical plane; and a laser cuttinghead movable relative to the sheet metal in the horizontal or verticalplane. Furthermore, the invention is applicable for use in cuttingmachines which comprise a laser focusing head or a plasma or water jetcutting head instead of the laser cutting head of the laser cuttingmachine.

What is claimed is:
 1. A method for cutting a window in a sheet ofmaterial, especially sheet metal, comprising the steps of: (a) holdingthe sheet in a vertical plane; (b) cutting the sheet by using a cuttinghead capable of emitting a fluid while in use and moving the saidcutting head along a closed run that defines the outline of a piece ofwaste material contained within said window such that said run returnsto its starting point situated above a horizontal axis passing throughthe barycentre of said piece of waste material; and (c) by action of thefluid emitted from the cutting head, dropping the piece of wastematerial from the window in the sheet of material held in the verticalplane such that the waste material falls on a side of the sheet oppositeto a side on which the cutting head is located during step (b).
 2. Amethod in accordance with claim 1, wherein said run returns to itsstarting point situated in the vicinity of a vertical axis passingthrough the barycentre of the piece of waste material.
 3. A method inaccordance with claim 1, wherein said method is used for cutting awindow of a generally concave shape or comprising parts that are eitherprotruding or recessed in a sheet of material, especially sheet metal,characterized in that the cutting of the window is subdivided intocutting several pieces of waste material each of which is devoid ofprotrusions or recesses and, further, that each of said pieces of wastematerial is cut by using steps (b) and (c).
 4. A method in accordancewith claim 2, wherein said method is used for cutting a window of agenerally concave shape or comprising parts that are either protrudingor recessed in a sheet of material, especially sheet metal,characterized in that the cutting of the window is subdivided intocutting several pieces of waste material each of which is devoid ofprotrusions or recesses and, further, that each of said pieces of wastematerial is cut by using steps (b) and (c).